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Date: Thu, 08 Oct 1998 18:50:41 -0500
From: Snowbird <snbird@ibm.net>
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Subject: Re: mixture control question
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Jim Sokoloff wrote:
 
> sarangan@unm.edu (Andrew M. Sarangan) writes:
> > As you lean the mixture the EGT will increase up to a point. After
> > that it will decrease. At peak EGT the engine will be at its highest
> > fuel efficiency.  But for better engine longevity, it is recommended
> > that you run the mixture slightly richer than the peak EGT. 

AFAIK, Textron-Lycoming makes no recommendation regarding running
rich of peak for better engine longevity.  Their recommendations 
for better longevity are: 1) run at <65% power 2) CHT <400 deg F
3) oil temperature 165-220 deg F.   Can't speak for Continental.

> > to check your POH for this, but for the C-210 I fly it should be
> > about 50F cooler than peak.
 
> This is (like many things in aviation) the subject of some
> debate. Continental at least authorizes (I think recommends, but I
> can't be sure) continuous operation at peak EGT for 65% or less power,
> provided CHT limits are observed. I believe Lycoming's recommendations
> are similar (and if I'm wrong, you'll surely read about it the flaming
> I receive below... :-) )

No flames.  The suggestion that anyone interested in such issues
check out Gregory Travis' great contribution to general aviation
at http://www.prime-mover.org.  In particular look at Lycoming's
Service Instruction 1094D, "Fuel Mixture Leaning Procedures", at
http://www.prime-mover.org/Aviation/Bulletins/si1094.html

Basically, there are two leaning procedures authorized: leaning
for best power (below 75% power at any altitude and at any throttle
setting when above 5000 ft DA) and leaning for best economy (below 
75% power).  

Best power leaning is for max rpm/airspeed and is approximately
100 degrees rich of peak EGT.

Best economy leaning is peak EGT, enrichened only as necessary
to prevent engine roughness (usually caused by some cylinders
peaking before the others, and not always the cylinder the gauge
is on if it's only one cylinder).

Due to copyright issues, Greg was unable to make Continental's
service instructions and bullitens available on line.

Snowbird


